Why do most people try to do business with the references of others?

[Pandazel]

I wonder why some people try to do business with references from others in SEO, web design, graphic design, and article services. Sometimes, I see graphic designers using references that I happen to come across online being used by others as well. This also applies to those providing web design and SEO article services. So, why do they feel the need to resort to such deceptive practices?